The present invention relates to a means for vertically moving a ram in a compression molding machine for rubber, plastic, etc.
Conventional means for vertically moving a ram in a compression molding machine include double-cylinder constructions comprising an outer cylinder and a ram slidably fitted therein, said ram having a hollow part in the center thereof and serving also as an inner cylinder. The double-cylinder constructions have been employed in large compression molding machines having a ram of a large diameter because the double-cylinder constructions have the advantage that they make it possible to use a hydraulic pump having a smaller capacity. FIG. 3 shows a typical conventional double-cylinder construction in a compression molding machine, which construction comprises an outer cylinder 1 and a ram or an inner cylinder 3 slidably fitted therein, said ram 3 being provided at the lower end thereof with a large-diameter portion 2, said ram 3 having a hollow part 4 in the center thereof, a rod 6 being fitted in said hollow part 4 so as to penetrate the bottom 5 of said outer cylinder 1, said rod 6 being slidable ralative to said ram 3 and immovably fixed to the bottom of said outer cylinder 1, said rod 6 being provided in the center thereof with an oil passage 7 penetrating the rod 6 from end to end. A space formed by the lower surface of said large-diameter portion 2 of the ram 3, the inner surface of said outer cylinder 1 and the periphery of said rod 6 serves as a lower oil reservoir 8. A portion of said hollow part 4 of the ram 3 over the rod 6 serves as a ram raising oil reservoir 9. A space formed by the periphery of the ram 3 and the inner surface of the cylinder 1 serves as a ram lowering oil reservoir 10. Numeral 11 represents a check valve, and numeral 12 represents an oil tank.
In the double-cylinder construction described above, the ram 3 will be raised when an oil pressure is applied to the ram raising oil reservoir 9 through the oil passage 7 within the rod 6. The ram 3 will be lowered if an oil pressure is applied to the ram lowering oil reservoir 10 when the ram 3 is in a raised position.
In the conventional means for vertically moving a ram in a compression molding machine, the ram is vertically moved by means of oil pressure only, and all oil used for vertically moving the ram is supplied from outside. Therefore, it is not necessarily possible to make external hydraulic apparatuses including the oil tank satisfactorily small and less expensive.